For example, an automatic transmission disclosed in Patent document 1 (hereinafter referred to as “conventional automatic transmission”) is known as an automatic transmission of the above kind. Patent document 1 discloses an automatic transmission which is equipped with a reduction double planetary gear train in which a common sun gear directly connected to an input shaft is in mesh with a first ring gear via a small-diameter pinion of a stepped pinion supported by a carrier and is in mesh with a second ring gear via a large-diameter pinion of the stepped pinion, a shifting double planetary gear train in which a sun gear of a first single pinion planetary gear train and a sun gear of a second single pinion planetary gear train are directly connected to each other and a carrier of the first single pinion planetary gear train and a ring gear of the second single pinion planetary gear train are directly connected to each other, a first clutch for selectively connecting the input shaft to the directly connected sun gears of the shifting double planetary gear train, a second clutch for selectively connecting the input shaft to the directly connected carrier and ring gear of the shifting double planetary gear train, a first brake for selectively fixing the first ring gear of the reduction double planetary gear train, a second brake for selectively fixing the second ring gear of the reduction double planetary gear train, a third brake for selectively fixing the carrier of the reduction double planetary gear train and a ring gear of the first single pinion planetary gear train which are directly connected to each other, a fourth brake for selectively fixing the directly connected carrier and ring gear of the shifting double planetary gear train, and an output shaft which is directly connected to a carrier of the second single pinion planetary gear train. Rotation of the input shaft is transmitted to the output shaft while shifting is made between forward eight shift stages and a backward shift stage.
[Patent document 1] JP-A-2002-213545